Motor drive device and air conditioner

Abstract

A motor drive device that drives motors with one inverter includes a step-out control unit that detects step-out in which the operating frequency of at least one of the motors does not match the inverter output frequency, or the operating frequency of at least one of the motors does not match the operating frequency of another one of the motors, and stops the motors by switching an energization state of the inverter when at least one of the motors is out of step.

The invention claimed is: 
     
       1. A motor drive device comprising:
 one inverter that drives a plurality of motors; and 
 a step-out control unit that detects step-out in which an operating frequency of at least one of the motors does not match an inverter output frequency, or an operating frequency of at least one of the motors does not match an operating frequency of another one of the motors, and stops the plurality of motors by switching an energization state of the inverter when at least one of the motors is out of step, wherein 
 when at least one of the motors is out of step, first control is performed to apply a voltage for step-out control to the motors. 
 
     
     
       2. The motor drive device according to  claim 1 , wherein
 the step-out control unit detects that the motors are out of step based on a change in a direction of a motor current flowing through each phase of the plurality of motors, a detected value of the motor current, or an estimated speed value of the plurality of motors. 
 
     
     
       3. The motor drive device according to  claim 1 , wherein
 the step-out control unit detects that the motors are out of step using at least two of a change in a direction of a motor current flowing through each phase of the plurality of motors, a detected value of the motor current, and an estimated speed value of the plurality of motors. 
 
     
     
       4. The motor drive device according to  claim 1 , wherein
 in the first control, a harmonic component is superimposed on a motor current flowing through each phase of the motors. 
 
     
     
       5. The motor drive device according to  claim 1 , wherein
 in the first control, a current command value that is used in motor control is controlled to zero. 
 
     
     
       6. The motor drive device according to  claim 1 , wherein
 when at least one of the motors is out of step, the first control is performed in response to determining that the number of motors that are out of step is different from the number of motors that have been in operation. 
 
     
     
       7. The motor drive device according to  claim 6 , wherein
 when at least one of the motors is out of step, in response to a peak value of a current flowing through each phase of the motor falling below a current threshold after the first control is performed, third control is performed to cut off an output voltage from the inverter. 
 
     
     
       8. The motor drive device according to  claim 6 , wherein
 when at least one of the motors is out of step, in response to an estimated speed value of the motor falling below a speed threshold after the first control is performed, third control is performed to cut off an output voltage from the inverter. 
 
     
     
       9. The motor drive device according to  claim 6 , wherein
 when at least one of the motors is out of step, in response to an elapsed time from step-out detection exceeding a time threshold after the first control is performed, third control is performed to cut off an output voltage from the inverter. 
 
     
     
       10. An air conditioner comprising the motor drive device according to  claim 1 . 
     
     
       11. A motor drive device comprising:
 one inverter that drives a plurality of motors; and 
 a step-out control unit that detects step-out in which an operating frequency of at least one of the motors does not match an inverter output frequency, or an operating frequency of at least one of the motors does not match an operating frequency of another one of the motors, and stops the plurality of motors by switching an energization state of the inverter when at least one of the motors is out of step, wherein 
 when at least one of the motors is out of step, second control is performed to bring one or more of upper-arm switching elements or lower-arm switching elements of the inverter to a conductive state. 
 
     
     
       12. The motor drive device according to  claim 11 , wherein
 when at least one of the motors is out of step, the second control is performed in response to determining that the number of motors that are out of step is equal to the number of motors that have been in operation. 
 
     
     
       13. The motor drive device according to  claim 12 , wherein
 when at least one of the motors is out of step, in response to a peak value of a current flowing through each phase of the motor falling below a current threshold after the second control is performed, third control is performed to cut off an output voltage from the inverter. 
 
     
     
       14. The motor drive device according to  claim 12 , wherein
 when at least one of the motors is out of step, in response to an estimated speed value of the motor falling below a speed threshold after the second control is performed, third control is performed to cut off an output voltage from the inverter. 
 
     
     
       15. The motor drive device according to  claim 12 , wherein
 when at least one of the motors is out of step, in response to an elapsed time from step-out detection exceeding a time threshold after the second control is performed, third control is performed to cut off an output voltage from the inverter. 
 
     
     
       16. An air conditioner comprising the motor drive device according to  claim 11 . 
     
     
       17. A motor drive device comprising:
 one inverter that drives a plurality of motors; and 
 a step-out control unit that detects step-out in which an operating frequency of at least one of the motors does not match an inverter output frequency, or an operating frequency of at least one of the motors does not match an operating frequency of another one of the motors, and stops the plurality of motors by switching an energization state of the inverter when at least one of the motors is out of step, wherein 
 when at least one of the motors is out of step, switching between first control, second control, and third control is performed on a time-series basis, the first control being to apply a voltage for step-out control to the motors, the second control being to bring one or more of upper-arm switching elements or lower-arm switching elements of the inverter to a conductive state, the third control being to cut off an output voltage from the inverter. 
 
     
     
       18. An air conditioner comprising the motor drive device according to  claim 17 .